1. Field
The present description relates to a method, system, and computer program for mapping source-target relationships in a storage area network.
2. Description of Related Art
One or more hosts may store large quantities of data in a group of storage units, which is typically controlled by a storage controller. An example of such a storage controller is the IBM TotalStorage® Enterprise Storage Server® (ESS). A storage controller such as the ESS may provide a number of functions accessible by the hosts for protecting data, backing up the data, and making the data available for use.
Amongst the functions which may be provided by a storage controller is a data preservation function which can preserve an identified set of data at a particular point in time. For example, the ESS storage controller supports a data preservation function referred to as “FlashCopy” which enables a copy to be made of a set of tracks in a source volume. One feature of such data preservation functions is that the data of the copy is frequently made immediately available for read or write access. The identified data may be for example, a set of tracks which can consist of an entire volume, a data set, or just a selected set of tracks, for example.
In one mode of a data preservation function, a copy of all of the data to be preserved at the particular point in time, is made by copying the identified data from identified tracks of the source volume to identified tracks of the target volume, typically in a background copy mode. In this manner, a relationship is established between those identified tracks on the source volume and corresponding tracks on the target volume, in response to a data preservation request. The data preservation relationship may be initiated in response to the data preservation request and may be terminated and deleted when the background copy completes or in response to a withdrawal command.
However, for some data storage operations, copying all of the data to be preserved at a point in time may not be suitable. For example, some storage units are configured for improved data storage efficiency. Examples of efficiency configurations include the “Track Space Efficient” and “Extent Space Efficient” volume configurations often used in ESS data storage systems. A track “extent” typically contains a beginning track, an ending track, and all the tracks between the beginning track and the end track.
In such volume efficiency configurations, a different mode of operation may be used for a data preservation function. For example, instead of copying all of the data to be preserved at a point in time, a “block on write” paradigm may be followed.
As noted above, the data preservation relationship may be initiated in response to a data preservation request and may end when the background copy completes or in response to a withdrawal command. There are various reasons for withdrawing a FlashCopy relationship. For example, there might no longer be a need for the FlashCopy relationship. In those and other situations, the withdrawal command may be used to delete the relationship between the source and target.
In many prior storage systems, a relationship may be deleted or removed immediately in response to a withdrawal command. Hence, a new relationship which encompasses tracks of a prior relationship may frequently be rapidly established in such systems following a withdrawal command of the prior relationship.